CZ2000200A3 - Glass ceramic materials, the method of their preparation and use - Google Patents

Abstract

The present invention refers to glass-ceramics consisting of the mixtures (I): ZrO2-SiO2-Me<II>O, or (II) SiO2-Me<III>O2-Me<II>O, wherein: Me<II> is chosen in the group consisting of: Ca, Ba, Mg, Zn or mixture thereof; Me<III> is chosen in the group consisting of Al, B or mixtures thereof; each of the above said constituents being present in determined quantities; the invention refers also to a process for preparing the glass-ceramics above defined; porcelain stonewares and glazes containing them and their use for preparing ceramic items.

Description

Technical area

The present invention relates to glass-ceramic materials consisting of mixtures (I) or (II):

(I) ZrO ₂ -SiO ₂ -Me ^II O (II) SiO ₂ -Me ₂ ^III O3~Me ^II O wherein in mixture (I): Me ¹¹ = Ca, Ba, Mg, Zn or their mixtures and the weight percentage of each component is: ZrO2 5-25% SiO2 45-75% Me^O 15-45% and in mixture (II) Me ¹¹ is according to the above definition Me ¹¹¹ = Al, B or their mixtures and the weight percentage of each of the above components is: SiO2 30-65% Me ₂ ⁱⁿ O ₃ 5-25% Me ^XI 0 5-40% and are characterized in that the glass-ceramic materials are obtained in the form of powders.

State of the art

It is known that glass is an amorphous material obtained by melting crystalline compounds, followed by cooling the molten material.

In contrast, glass-ceramic materials (hereinafter referred to as GC) are glass systems that, when heated to a temperature T1 higher than their glass transition temperature Tg, form nuclei (homogeneous or heterogeneous nucleation) with subsequent crystal growth.

Porcelain stoneware (also defined as a ceramic material with absorption < 0.5% (according to ISO 13006, BIA supplement) is a ceramic material prepared from natural crystalline products that partially melt and transform into new crystalline phases during sintering. These products are prepared from a mixture of clay minerals, fluxes and possibly also fusion promoters.

Glaze is a ceramic product consisting of fluxes and silica-based glasses that are ground into granules of the desired dimensions and then applied to a suitable substrate, where they are heated so that the ground granules melt (fully or partially), covering the surface of the substrate.

All of the above-mentioned products with a glassy surface provide porous materials with impermeability and better physicochemical properties (better resistance to chemical agents, abrasion, etc.). In addition, they play an important role as aesthetic materials due to the use of lead-based fluxes, fillers (which are dispersions of, for example, tin dioxide or zirconium silicate, added in the form of crystals with a specific granulometry) and color pigments.

JP-A-62 072539 describes a crystallized glass prepared by shaping a glass containing SiO ₂ and ZrO ₂ as main components and crystallization thereof in the temperature range of 750-1300 °C in order to form tetragonal zirconium oxide in the glass.

However, known materials do not fully satisfy the market needs in terms of physicochemical properties and opacity (and the resulting whiteness index) are also not always fully satisfactory, as they result in final products that are not aesthetically suitable for some applications; in addition, known methods of producing glass-ceramic materials are expensive and result in unnecessary energy losses.

The essence of the invention

The invention solves the above problems thanks to new glass-ceramic materials with the above composition and characterized in that they are obtained in the form of powders.

The glass-ceramic materials of the invention can be used as such for the production of ceramics, or they can be added to materials commonly used for the preparation of porcelain stoneware or glazes.

The use of glass-ceramic materials according to the invention makes it possible (thanks to their in situ crystallization) to introduce exceptional opacity into glazes, resulting in a higher whiteness index (WI) compared to the index obtained when using normal glazes added to glass and, in addition, thanks to the chemical stability and higher mechanical resistance of the crystalline phase recrystallized on the surface of the glaze, they give the substrate physicochemical properties better than those of traditional glazes.

The glass-ceramics according to the invention also provide the possibility of creating ceramics directly from molten raw material, which can be shaped into the desired shape, or of preparing the necessary ceramic products by casting suspensions into tapes (tape casting) or by hot or cold pressing of powders.

The following Table I lists preferred glass-ceramic materials according to the invention (the proportion of components is given in weight percent):

Table I

Combined. Si0 ₂ CaO ZrO ₂ BaO ZnO MgO A1 ₂ O ₃ b ₂ o ₃ GC. 1 55 33 12 GC.2 52.5 31.3 16.2 GC.3 55 21 12 12 GC.4 52.3 21.9 16.4 9, 4

GC.5 55 11 12 11 11 GC.6 51.6 39.7 8.7 GC.7 37.8 17.63 37.98 6.59 GC.8 47.95 23.55 9.3 19.2 GC. 9 41 0.5 30 20.5 8 GC.10 36.77 47.05 9.75 6.43 GC.ll 61 24 15

The glass-ceramic materials according to the invention can be prepared in a manner essentially similar to the method of producing porcelain stoneware, which consists of grinding, mixing and pressing powders (and subsequent firing of the pressed materials), with the difference that in this case the powders consist only of glass (so that the starting crystalline materials used in the production of porcelain stoneware are absent).

However, it is important to carry out the firing stage in well-defined and controlled thermal cycles guaranteeing the desired properties.

In particular, after determining the Tg (glass transition temperature) and Tc (crystallization temperature) of this material by conventional methods, the following temperature cycle procedure must be followed: the powder mixture is heated from the initial room temperature at a temperature increase rate of 10-30 °C per minute up to a temperature of 350 °C (in order to remove organic impurities by conventional methods), then the heating temperature is increased at a rate of 10-30 °C per minute to Tg and maintained at this temperature for 0 to 120 minutes, then the temperature is increased at a rate of 10-30 °C per minute to Tc, at which it is maintained for 0 to several hours, for example up to seven hours, preferably 0 to 4 hours, and it is possible to continue further at a temperature increase rate of 10-30 °C per minute until the next Tc and so on until the final Tc; after the heating is completed (i.e. when the highest Tc has been reached), the material is cooled back to room temperature.

As mentioned above, the glass-ceramic materials of the invention can be added to the materials normally used for the production of porcelain stoneware; the addition of the glass-ceramic materials of the invention allows the ceramics to be produced in a manner normally used for the production of porcelain stoneware, resulting in significant energy savings.

The glass-ceramic material according to the invention is added, for example, to a traditional mixture of starting materials for the production of porcelain stoneware; the mixture is fed into an Alsing ball mill (continuous or discontinuous) and ground in the presence of water to form a suspension, which is dried using an atomizer to form hollow grains. These grains are shaped into tiles by a traditional pressing method. The tiles are dried and fired in a traditional kiln at a temperature of 900-1230. °C to form the final product. The tiles obtained are composed of sintered and crystallized materials and a residual glassy phase, as can be demonstrated by mineral and X-ray analysis of the surface of the tiles.

It is preferred that the glass-ceramic materials are added to the traditional materials in an amount between 5% and 65% by weight. Table 2 gives an example of the composition of the mixture of starting materials (expressed in weight percent of metal oxides) used in the production of the glass-ceramic materials according to the invention in the amounts indicated:

Table 2

SI0 ₂ 40-80 A12O3 5-40 MgO 0.1-10 CaO 0.1-10 At ₂ 0 0.1-10

To ₂ 0 0.1-10

In this context, it was surprisingly found that other already known glass-ceramic materials can also be added to the traditional starting materials for the production of porcelain stoneware with similarly favorable results.

Examples of already known glass-ceramic materials (a-d) which can be used for the above purpose are given in the following Table 3 (the percentage is given in weight percent).

Table 3

Sklokeram. mat. Ltd. A1 ₂ O ₃ SiO ₂ Ltd. _K2O MgO and 30-40 25-30 30-45 b 40-50 10-25 30-40 c 15-25 60-70 10-20 d 20-25 10-25 45-55 5-15

Glazes can be produced by methods traditionally used in the production of glazes. The glass-ceramic material according to the invention and the starting material usually used for the preparation of ceramic glazes (which are essentially the same as the materials used for the preparation of porcelain stoneware with the addition of fluxes such as frits, borates or lead oxides and others) are charged in appropriate proportions into an Alsing ball mill in the presence of water and ground to form the so-called glaze, which is applied with an air gun, under pressure to the lower expanded part of the mold, using a threaded jaw, by screen printing or on a traditional raw or first-fired substrate, obtained by pressing atomized or dry-ground powders. The glaze, after drying and/or granulation, is deposited on the surface of the substrate by gravity and fixed with suitable organic binders (ligants). The substrate is fired at 900°C to 1230°C in a rapid firing furnace or in a tunnel kiln (continuous or discontinuous) to produce a final product in which the glass-ceramics contained have undergone controlled crystallization. The glazed tiles thus obtained exhibit a glassy and crystalline part, characterised by a well-defined microstructure as demonstrated by SEM and X-ray diffractometry.

It is preferred that the glass-ceramic materials according to the invention are added to the traditional materials in an amount between 5% and 60% by weight.

Examples of embodiments of the invention

EXAMPLE 1

Preparation of porcelain stoneware (corresponds to example 2 in table 4)

GC2 (50% of the total weight) is charged into the Alsing ball mill together with the traditional starting material (see example 2 in Table 4) (50% of the total weight).

Water (up to 50% by weight of the material in the mill) and 0.4% by weight of sodium tripolyphosphate as a plasticizer are added.

The mixture is ground until the remainder of the suspension on a sieve with a mesh size of 63 micrometers reaches only 0.7 - 1% by weight.

Under mechanical stirring, the suspension is poured into a tank and then spray-dried to a water content of about 6%, which is the ideal moisture content for subsequent pressing.

The wet powder is pressed at a pressure of 250 - 500 kg/cm ² into the required shapes and heated in a furnace at 1230 °C.

By repeating the method described in Example 1, but using the products and quantities indicated in the following

Tables 4 - 13, other porcelain stonewares were obtained; glass-ceramic materials are listed with reference to Table 1, with the amounts expressed in % by weight:

Table 4

Traditional materials Glass-ceramic materials according to the invention Glass-ceramic materials, % Traditional materials, % Si0 ₂ 76.0 A1 ₂ O ₃ 17.8 MgO 0.8 CaO 1.0 Na ₂ O 2.3 K ₂ O 2.1 GC 2 5 95 Si0 ₂ 54.6 AI2O3 41.8 MgO 0.2 CaO 0.7 Na ₂ O 0.4 K ₂ O 2.3 GC 2 50 50 Si0 ₂ 54.5 A1 ₂ O ₃ 42.5 MgO 0.2 CaO 0.5 Na ₂ O 0.3 K ₂ O 2.0 GC 2 65 35

Table 5

Traditional materials Glass-ceramic materials according to the invention Glass-ceramic materials, $ Traditional materials, $ SiO2 73.5 GC 3 5 95

A1 ₂ O ₃ 18.1 MgO 0.8 CaO 1.0 Na ₂ O 3.5 K ₂ O 3.1 Si0 ₂ 84.0 M ₂ O ₃ 10.3 MgO 0.3 CaO 0.7 Na ₂ O 2.4 K ₂ O 2.3 GC 3 50 50 Si0 ₂ 56.3 A1 ₂ O ₃ 39.5 MgO 0.3 CaO 0.6 Na ₂ O 1.3 K ₂ O 2.0 GC 3 65 35

Table 6

Traditional materials Glass-ceramic materials according to the invention. Glass-ceramic materials, % Traditional . materials, % Si0 ₂ 74.8 GC 4 5 95 A1 ₂ O ₃ 20.1 MgO 0.7 CaO 1.1 Na ₂ O 1.2 _K2O2.1 Si0 ₂ 61.3 GC 4 50 50 A1 ₂ O ₃ 35.3 MgO 0.3 CaO 0.1 Na ₂ O 1.2

_K2O1.8 Si0 ₂ 60.0 A1 ₂ O ₃ 37.0 MgO 0.2 CaO 0.8 Na ₂ O 1.0 K ₂ O 1.0 GC 4 65 35

Table 7

Traditional Glass-ceramic materials according to the invention Glass-ceramic materials, % Traditional materials, % materials Si0 ₂ 72.2 A1 ₂ O ₃ 18.5 MgO 0.9 CaO 1.3 Na ₂ O 4.0 K ₂ O 3.1 GC 5 5 95 Si0 ₂ 81.5 A1 ₂ O ₃ 12.0 MgO 0.2 CaO 1.0 Na ₂ O 2.2 K ₂ O 3.1 GC 5 50 50 Si0 ₂ 58.5 A1 ₂ O ₃ 37.3 MgO 0.3 CaO 0.6 Na ₂ O 1.0 K ₂ O 2.3 GC 5 65 35

Table 8

Traditional materials Glass-ceramic materials according to the invention Glass-ceramic materials, % Traditional materials, Ϊ SiO2 76.0 A1 ₂ O ₃ 17.8 MgO 0.8 CaO 1.0 Na ₂ O 2.3 K ₂ O 2.1 GC 9 5 95 Si0 ₂ 62.8 A1 ₂ O ₃ 25.8 MgO 0.2 CaO 0.9 Na ₂ O 7.1 K ₂ O 3.2 GC 9 50 50 Si0 ₂ 63.6 A1 ₂ O ₃ 31.6 MgO 0.3 CaO 1.1 Na ₂ O 1.0 K ₂ O 2.4 GC 9 65 35

Table 9

Traditional materials Glass-ceramic materials according to the invention Glass-ceramic materials, % Traditional materials, % SiO ₂ 75.9 AI2O3 17.7 MgO 0.8 CaO 1.0 Na ₂ O 2.5 GC 6 5 95

_K2O2.1 Si0 ₂ 72.8 GC 6 50 50 A1 ₂ O ₃ 10.1 MgO 6.7 CaO 0.2 Na ₂ O 7.5 _K2O2.7 SiO2 f o GC 6 65 35 A1 ₂ O ₃ 20.0 MgO 2.2 CaO 0.4 Na ₂ O 7.8 _K2O2.6

Table 10

Traditional materials Glass-ceramic materials according to the invention Glass-ceramic materials, % Traditional materials, % Si0 ₂ 74.0 AI2O3 14.2 MgO 1.5 CaO 1.5 Na ₂ O 4.2 K ₂ O 4.6 GC 7 5 95 Si0 ₂ 72.6 A1 ₂ O ₃ 14.8 MgO 1.3 CaO 2.0 Na ₂ O 9.0 K ₂ O 0.3 GC 7 50 50 Si0 ₂ 65.9 Al ₂ O ₃ 23.6 GC 7 65 35

MgO 0.2 CaO 0.9 Na ₂ O 9.1 K ₂ O 0.3

Table 11

Traditional materials Glass-ceramic materials according to the invention Glass-ceramic materials, % Traditional materials, % Si0 ₂ 74.3 A1 ₂ O ₃ 15.8 MgO 1.5 CaO 2.2 Na ₂ O 3.7 K ₂ O 2.5 GC 8 5 95 Si0 ₂ 68.0 A1 ₂ O ₃ 26.8 MgO 2.2 CaO 0.4 Na ₂ O 1.0 K ₂ O 1.6 GC 8 50 50 Si0 ₂ 67.0 A1 ₂ O ₃ 28.0 MgO 1.8 CaO 1.2 Na ₂ O 0.3 K ₂ O 1.7 GC 8 65 35

Table 12

Traditional Glass ceramic mat. Glass ceramic Traditional

materials according to the invention materials, % materials, f SiO ₂ 74.0 A1 ₂ O ₃ 17.6 MgO 1.8 CaO 1.4 Na ₂ O 3.7 K ₂ O 1.5 GC 10 5 95 Si0 ₂ 69.0 A1 ₂ O ₃ 26.8 MgO 1.2 CaO 0.4 Na ₂ O 1.0 K ₂ O 1.6 GC 10 50 50 Si0 ₂ 67.9 A1 ₂ O ₃ 28.5 MgO 1.0 CaO 1.1 Na ₂ O 0.4 K ₂ O 1.1 GC 10 65 35

Table 13

Traditional materials Glass-ceramic materials according to the invention Glass-ceramic materials, i Traditional materials, § Si0 ₂ 78.0 A1 ₂ O ₃ 10.8 MgO 2.2 CaO 0.4 Na ₂ O 6.0 K ₂ O 2.6 GC 11 5 95 Si0 ₂ 70.1 Al ₂ O ₃ 14.9 GC 11 50 50

MgO 8.7 CaO 0, 1 Na ₂ O 4.3 _K2O 1, 9

Si0 ₂ 69, 0 A1 ₂ O ₃ 27, 3 MgO 1.0 CaO 1, 1 Na ₂ O l,o _K2O 0.9

GC 11

EXAMPLE 2

Preparation of glazes (corresponds to example 1 in table 14)

GC2 (30% by weight) was charged into a batch Alsing ball mill together with traditional starting materials (see Example 1 in Table 14) (50% by weight). Water (up to 50% by weight of the total weight of the material in the mill), sodium tripolyphosphate as a flow agent (0.4% by weight) and hydroxymethylcellulose (0.3%) as an organic binder (ligant) were added.

The mixture was ground until the residue of the suspension on a 16,000 micron mesh screen was about 2% by weight.

The suspension was applied in the lower expanded edge of the mold onto the pressed substrate under a pressure of 500 g - 2.5 kg, which was then heated in an oven to 1160 °C.

The other glazes were prepared by repeating the process described in Example 2 but using the products listed in the following Tables 14-23; the glass-ceramic materials are listed with reference to Table 1 and the amounts are expressed in % by weight.

Each table lists the starting materials and corresponding quantities for preparing two different glazes • « · · ··«· ·· • · · · · ·· • ·«·· < · · · • · · · · · ·

.............

(designated as glaze I and glaze II) based on the same glass-ceramic material according to the invention and the same traditional starting compounds, but using different amounts thereof.

Table 14

Traditional starting materials and/or frits Glass-ceramic materials Glaze I Glaze II GC 2 30 50 Si0 ₂ 54.0 A1 ₂ O ₃ 33.0 MgO 0.3 CaO 0.7 Na ₂ O 8.0 K ₂ 0 4.0 70 50

Table 15

Traditional starting materials and/or frits Glass-ceramic materials Glaze I Glaze II GC 3 30 50 Si0 ₂ 60.0 A1 ₂ O ₃ 31.8 MgO 0.2 CaO 0.8 Na ₂ 0 6.2 K ₂ O 1.0 70 50

Table 16

Traditional starting materials and/or frits Glass-ceramic materials Glaze I Glaze II GC 4 30 50 Si0 ₂ 60.0 A1 ₂ O ₃ 31.2 MgO 0.4 CaO 0.8 Na ₂ O 6.0 K ₂ O 1.6 70 50

Table 17

Traditional starting materials and/or frits Glass-ceramic materials Glaze I Glaze II GC 5 30 50 Si0 ₂ 60.0 A1 ₂ O ₃ 28.0 MgO 0.0 CaO 5.0 Na ₂ O 3.0 K ₂ O 2.0 SnO ₂ 2.0 70 50

Table 18

Traditional starting materials and/or frits Glass-ceramic materials Glaze I Glaze II GC 9 30 50 Si0 ₂ 58.0 A1 ₂ O ₃ 18.0 MgO 2.5 CaO 10.5 70 50

Na ₂ O 6.0 K ₂ O 5.0

Table 19

Traditional starting materials and/or frits Glass-ceramic materials Glaze I Glaze II GC 6 30 50 Si0 ₂ 59.0 A1 ₂ O ₃ 10.0 70 50 MgO 1.0 CaO 7.0 Na ₂ O 8.0 _K2O3.0 ZrO ₂ 12.0

Table 20

Traditional starting materials and/or frits Glass-ceramic materials Glaze I Glaze II GC 7 30 50 Si0 ₂ 60.0 A1 ₂ O ₃ 17.1 MgO 2.4 Na ₂ O 6.2 K ₂ O 4.3 ZrO ₂ 8.0 TiO ₂ 2.0 70 50

Table 21

Traditional starting materials and/or frits Glass-ceramic materials Glaze I Glaze II

GC 8 30 50 Si0 ₂ 54.0 AI2O3 26, 0 70 50 MgO 0.1 CaO 8.5 The best 11, 0 _K2O 0, 2 _TiO2 0.2

Table 22

Traditional starting materials and/or frits Glass-ceramic materials Glaze I Glaze II GC 10 30 50 Si0 ₂ 62.0 AI2O3 6.3 MgO 1.3 CaO 14.0 Na ₂ O 0.5 K ₂ O 5.6 ZnO 10.3 70 50

Table 23

Traditional starting materials and/or frits Glass-ceramic materials Glaze I Glaze II GC 11 30 50 Si0 ₂ 50.0 Al ₂ O ₃ 25.0 70 50

MgO 10.0 Na ₂ O 7.0 K ₂ O 6.0 TiO ₂ 2.0

EXAMPLE 3

Glass ceramic preparation

In this case, the powder is prepared according to Example 1, but only GC2 is used.

The tiles of Example 1 were prepared using the thermal cycle C1 shown in Table 24, which also shows the Tg, _Tc and _Tc2 of the starting materials (GC2).

Table 25 lists the thermal cycles for the preparation of compound GC8 and also lists the _Tg and _Tc of compound GC8.

All glass-ceramic materials obtained by the described methods showed a typical surface microstructure demonstrating several crystalline and glassy phases.

Table 24

Default product. GC2:

Tg = 825 °C

Temp = 966 °C

Tc2 = 1025 °C

Thermal cycles used:

B1 Cl C2 Degree of mines Total time, min T (’C) Degree of mines Total time, min T (’C) Degree of mines Total time, min T (’C) 0 0 25 0 0 25 0 0 25 35 35 350 35 35 350 35 35 350

30 65 350 30 65 350 30 65 350 55 120 900 55 120 900 55 120 900 30 150 900 30 150 900 30 150 900 8 158 980 8 158 980 25 175 1150 30 188 980 30 188 980 30 205 1150 17 205 1150 22 210 1200 30 205 1150 30 235 1150 30 240 1200

Table 25

GC8 starting material:

Tg = 740 °C

Tc = 934 °C

Thermal cycles used:

B1 Cl C2 Degree of mines Total time, min T (“O Degree of mines Total time, min T (°C) Degree of mines Total time, min T (’C) 0 0 25 0 0 25 0 0 25 35 35 350 35 35 350 ³⁵ 35 350 30 65 350 30 65 350 30 65 350 44 109 790 44 109 790 44 109. 790 30 139 790 30 139 790 30 139 790 16 155 950 26 165 1050 36 175 1150 30 185 950 30 195 1050 30 205 1150

Claims (11)

1. Glass-ceramic materials, characterized in that they consist of mixtures (I) and (II): (I) ZrO ₂ -SiO ₂ -Me ^i:i: O (II) SiO ₂ -Me ₂ ^III O3-Me ^II O wherein in mixture (I): Me ¹¹ is selected from the group consisting of: Ca, Ba, Mg, Zn or mixtures thereof and the weight percentage of each component is: ZrO2 = 5-25% SiO ₂ =45-75%' Me ^IX O = 15-45' % ' and in mixture (II) Me ¹¹ corresponds to the above definition Me ¹¹¹ is selected from the group consisting of Al, B or mixtures thereof and the weight fraction of each of the above components is: SiO2 = 30-65% Me2 ^TII O3 = 5-25% Me ⁿ 0 = 5-40% 2. Glass-ceramic materials according to claim 1, characterized in that they have the composition (in % (55:33:12) (52.5:31.3:16.2) (55:21:12:12) (52.3:21.9:16.4:9.4) (55:11:12:11:11) (51.6:39.7:8.7) (37.8:17.63:37.98:6.59) by weight): SiO ₂ -CaO-ZrO ₂ SiO ₂ -CaO-ZrO ₂ SiO ₂ -CaO-ZrO ₂ -BaO SiO ₂ -CaO-ZrO ₂ -ZnO SiO ₂ -CaO-ZrO ₂ -BaO-MgO SiO ₂ -ZnO-Al ₂ O ₃ -CaO-BaO-Al ₂ O ₃ SiO ₂ -CaO-MgO-Al ₂ O ₃ (47.95:23.55:9.3:19.2) SiO ₂ -CaO-ZnO-Al ₂ O ₃ -B ₂ O ₃ (41:0.5:30:20.5:8) SiO ₂ -BaO-MgO-Al ₂ O ₃ (36.77:47.05:9.75:6.43) SiO ₂ -CaO-Al ₂ O ₃ (61:24:15) 3. A method for preparing glass-ceramic materials according to claims 1 and 2, characterized in that the starting materials are subjected to the usual grinding/mixing/pressing steps carried out in methods for producing porcelain stoneware, and to a final firing step, which is carried out as follows: the pressed powder mixture is heated from the initial room temperature at a temperature increase rate of 10-30 °C per minute up to a temperature of 350 °C (in order to remove organic impurities), then the heating temperature is increased at a rate of 10-30 °C per minute up to T _g and is maintained at this temperature for 0 to 120 minutes, then the temperature is increased at a rate of 10-30 °C per minute up to T _c at which it is maintained for 0 to several hours and it is possible to further increase the temperature at a rate of 10-30 °C until the next T _c and so on until the final T _c ; After the heating is complete (that is, when the highest T _c has been reached), the material is cooled back to room temperature. 4. Porcelain stoneware, characterized in that it consists of a glass-ceramic material according to claim 1 and a traditional mixture of compounds used for the production of porcelain stoneware. 5. Porcelain stoneware according to claim 4, characterized in that the glass-ceramic material according to claim 1 represents 5 - 65% by weight, based on the total weight. 6. Porcelain stoneware according to claim 5, characterized in that It is noteworthy that the traditional mixture has the following mass composition: SIO ₂ 40-80 A12O3 5-40 MgO 0.1-10 CaO 0.1-10 Na ₂ O 0.1-10 K ₂ 0 0.1-10 7. Porcelain stoneware, characterized in that it consists of glass ceramics (a-d) having the following weight composition: SrO AI2O3 SiO ₂ ZrO K ₂ O MgO a 30-40 25-30 30-45 b 40-50 10-25 30-40 c 15-25 60-70 10-20 d 20-25 10-25 45-55 5-15 and az traditional mixture of compounds used in the production of porcelain stoneware. 8. Porcelain stoneware, characterized in that it consists of the following weight compositions: Traditional materials Inventive glass-ceramic materials Glass-ceramic materials, % Traditional materials, % Si0 ₂ 76.0 A1 ₂ O ₃ 17.8 MgO 0.8 CaO 1.0 Na ₂ O 2.3 K ₂ O 2.1 GC 2 5 95 Si0 ₂ 54.6 A1 ₂ O ₃ 41.8 MgO 0.2 CaO 0.7 Na ₂ O 0.4 K ₂ O 2.3 GC 2 50 50 Si0 ₂ 54.5 A1 ₂ O3 42.5 MgO 0.2 CaO 0.5 Na ₂ O 0.3 K ₂ O 2.0 GC 2 65 35 Traditional materials Glass-ceramic materials according to the invention Glass-ceramic materials, % Traditional materials, % SiO ₂ 73.5 A1 ₂ O ₃ 18.1 MgO 0.8 CaO 1.0 Na2O 3.5 K ₂ O 3.1 GC 3 5 95 Si0 ₂ 84.0 A1 ₂ O ₃ 10.3 MgO 0.3 CaO 0.7 Na ₂ O 2.4 K ₂ O 2.3 GC 3 50 50 Si0 ₂ 56.3 AI2O3 39.5 MgO 0.3 CaO 0.6 Na ₂ O 1.3 K ₂ O 2.0 GC 3 65 · 35 Traditional materials Inventive glass-ceramic materials Glass-ceramic materials, % Traditional materials, % Si0 ₂ 74.8 A1 ₂ O ₃ 20.1 MgO 0.7 CaO 1.1 Na ₂ O 1.2 K ₂ O 2.1 GC 4 5 95 Si0 ₂ 61.3 A1 ₂ O ₃ 35.3 MgO 0.3 CaO 0.1 Na ₂ O 1.2 K ₂ O 1.8 GC 4 50 50 Si0 ₂ 60.0 AI2O3 37.0 MgO 0.2 CaO 0.8 Na ₂ O 1.0 K ₂ O 1.0 GC 4 65 35 Traditional materials Inventive glass-ceramic materials Glass-ceramic materials, % Traditional materials, % Si0 ₂ 72.2 A1 ₂ O ₃ 18.5 MgO 0.9 CaO 1.3 Na ₂ O 4.0 K ₂ O 3.1 GC 5 5 95 SiO ₂ 81.5 A1 ₂ O ₃ 12.0 . MgO 0.2 CaO 1.0 Na ₂ O 2.2 K ₂ O 3.1 GC 5 50 50 Si0 ₂ 58.5 A1 ₂ O ₃ 37.3 MgO 0.3 CaO 0.6 Na ₂ O 1.0 K ₂ O 2.3 GC 5 65 35 Traditional materials Inventive glass-ceramic materials Glass-ceramic materials, % Traditional materials, % Si0 ₂ 76.0 A1 ₂ O ₃ 17.8 MgO 0.8 CaO 1.0 Na ₂ O 2.3 K ₂ O 2.1 GC 9 5 95 Si0 ₂ 62.8 A1 ₂ O ₃ 25.8 MgO 0.2 CaO 0.9 Na ₂ O 7.1 K ₂ O 3.2 GC 9 50 50 Si0 ₂ 63.6 A1 ₂ O ₃ 31.6 MgO 0.3 CaO 1.1 Na ₂ O 1.0 K ₂ O 2.4 GC 9 65 35 Traditional materials Inventive glass-ceramic materials Glass-ceramic materials, % Traditional materials, % Si0 ₂ 75.9 A1 ₂ O ₃ 17.7 MgO 0.8 CaO 1.0 Na ₂ O 2.5 K ₂ O 2.1 GC 6 5 95 Si0 ₂ 72.8 A1 ₂ O ₃ 10.1 MgO 6.7 CaO 0.2 Na ₂ O 7.5 K ₂ O 2.7 GC 6 50 50 Si0 ₂ 67.0 A1 ₂ O ₃ 20.0 MgO 2.2 CaO 0.4 Na ₂ O 7.8 K ₂ O 2.6 GC 6 65 35 Traditional materials Inventive glass-ceramic materials Glass-ceramic materials, % Traditional materials, % Si0 ₂ 74.0 A1 ₂ O ₃ 14.2 MgO 1.5 CaO 1.5 Na ₂ O 4.2 K ₂ O 4.6 GC 7 5 95 Si0 ₂ 72.6 A1 ₂ O ₃ 14.8 MgO 1.3 CaO 2.0 Na ₂ O 9.0 K ₂ O 0.3 GC 7 50 50 Si0 ₂ 65.9 A1 ₂ O ₃ 23.6 MgO 0.2 CaO 0.9 Na ₂ O 9.1 K ₂ O 0.3 GC 7 65 35 Traditional materials Inventive glass-ceramic materials Glass-ceramic materials, % Traditional materials, % Si0 ₂ 74.3 A1 ₂ O ₃ 15.8 MgO 1.5 CaO 2.2 Na ₂ O 3.7 K ₂ O 2.5 GC 8 5 95 Si0 ₂ 68.0 A1 ₂ O3 26.8 MgO 2.2 CaO 0.4 Na ₂ O 1.0 K ₂ O 1.6 GC 8 50 50 Si0 ₂ 67.0 A1 ₂ O ₃ 28.0 MgO 1.8 CaO 1.2 Na ₂ O 0.3 K ₂ O 1.7 GC 8 65 35 31, Traditional materials Inventive glass-ceramic materials Glass-ceramic materials, % Traditional materials, % Si0 ₂ 74.0 A1 ₂ O ₃ 17.6 MgO 1.8 CaO 1.4 Na ₂ O 3.7 K ₂ O 1.5 GC 10 5 95 Si0 ₂ 69.0 A1 ₂ O ₃ 26.8 MgO 1.2 CaO 0.4 Na ₂ O 1.0 K ₂ O 1.6 GC 10 50 50 Si0 ₂ 67.9 A1 ₂ O ₃ 28.5 MgO 1.0 CaO 1.1 Na ₂ O 0.4 K ₂ O 1.1 GC 10 65 35 Traditional materials Inventive glass-ceramic materials Glass-ceramic materials, % Traditional materials, % Si0 ₂ 78.0 A1 ₂ O ₃ 10.8 MgO 2.2 CaO 0.4 Na ₂ O 6.0 K ₂ O 2.6 GC 11 5 95 Si0 ₂ 70.1 A1 ₂ O ₃ 14.9 MgO 8.7 CaO 0.1 Na ₂ O 4.3 K ₂ O 1.9 GC 11 50 50 Si0 ₂ 69.0 A1 ₂ O ₃ 27.0 MgO 1.0 CaO 1.1 Na ₂ O 1.0 K ₂ O 0.9 GC 11 65 35 9. Ceramic glazes, characterized in that they consist of a glass ceramic according to claim 1 and a mixture of traditional compounds used in the production of glazes. 10. Ceramic glazes according to claim 9, characterized in that they consist of the following weight compositions: Traditional starting materials and/or frits Glass-ceramic materials Glaze I Glaze II GC 2 30 50 Si0 ₂ 54.0 A1 ₂ O ₃ 33.0 MgO 0.3 CaO 0.7 Na ₂ O 8.0 K ₂ O 4.0 70 50 Traditional starting materials and/or frits Glass-ceramic materials Glaze I Glaze II GC 3 30 50 Si0 ₂ 60.0 A1 ₂ O ₃ 31.8 MgO 0.2 CaO 0.8 Na ₂ O 6.2 K ₂ O 1.0 70 50 Traditional starting materials and/or frits Glass-ceramic materials Glaze I Glaze II GC 4 30 50 Si0 ₂ 60.0 A1 ₂ O ₃ 31.2 MgO 0.4 CaO 0.8 Na ₂ O 6.0 K ₂ O 1.6 70 50 Traditional starting materials and/or frits Glass-ceramic materials Glaze I Glaze II GC 5 30 50 Si0 ₂ 60.0 A1 ₂ O ₃ 28.0 MgO 0.0 CaO 5.0 Na ₂ O 3.0 K ₂ O 2.0 SnO ₂ 2.0 70 50 Traditional starting materials and/or frits Glass-ceramic materials Glaze I Glaze II GC 9 30 50 Si0 ₂ 58.0 A1 ₂ O ₃ 18.0 MgO 2.5 CaO 10.5 Na ₂ 0 6.0 K ₂ O 5.0 70 50 Traditional starting materials and/or frits Glass-ceramic materials Glaze I Glaze II GC 6 30 50 Si0 ₂ 59.0 A1 ₂ O ₃ 10.0 MgO 1.0 CaO 7.0 Na ₂ O 8.0 K ₂ O 3.0 ZrO ₂ 12.0 70 50 Traditional starting materials and/or frits Glass-ceramic materials Glaze I Glaze II GC 7 30 50 Si0 ₂ 60.0 A1 ₂ O ₃ 17.1 MgO 2.4 Na ₂ O 6.2 K2O 4.3 ZrO ₂ 8.0 TiO ₂ 2.0 70 50 Traditional starting materials and/or frits Glass-ceramic materials Glaze I Glaze II GC 8 30 50 Si0 ₂ 54.0 Α1 ₂ Ο ₂ 26.0 MgO 0.1 CaO 8.5 Na ₂ O 11.0 K ₂ O 0.2 TiO ₂ 0.2 70 50 Traditional starting materials and/or frits Glass-ceramic materials Glaze I Glaze II GC 10 30 50 Si0 ₂ 62.0 A1 ₂ O ₃ 6.3 MgO 1.3 CaO 14.0 Na ₂ O 0.5 K ₂ O 5.6 ZnO 10.3 70 50 . Traditional starting materials and/or frits Glass-ceramic materials Glaze I Glaze II GC 11 30 50 Si0 ₂ 50.0 A1 ₂ O ₃ 25.0 MgO 10.0 Na ₂ 0 7.0 K ₂ O 6.0 TiO ₂ 2.0 70 50 11. Ceramic materials consisting of the products claimed in claims 1, 4 and 9.